It is known in the field of optical communications to use optical wavelengths as optical carriers for carrying digital or analog information. Also, the different wavelengths may be used to discriminate one set or channel of information from another. When a plurality of wavelengths are coupled or multiplexed onto a single fiber, this is called wavelength division multiplexing (WDM). Use of such WDM increases the overall bandwidth of the system. For example, a single fiber carrying two wavelengths has twice the bandwidth of a fiber carrying a single wavelength. Generally, a large number of channels would be carried on one fiber. The closer the channel spacing, the greater the number of channels that may be transmitted over the fiber. Recently the International Telecommunications Union has proposed a Dense WDM (“DWDM”) network standard with optical signal channels having a frequency separation of 100 GHz (equivalent to a wavelength separation of about 0.8 nm), in order to ensure high utilization of the available optical bandwidth, and even denser standards are envisaged. The performance requirements for a DWDM network (such as those for bandwidth, cross talk, polarization dependent loss, polarization mode dispersion, insertion loss) are becoming more stringent. Additionally, it is anticipated that future efforts to increase capacity by reducing optical channel spacing will require additional improvements in optical system components
In co-pending PCT Application No. PCT IL02/00511, hereby incorporated by reference in its entirety, there is disclosed a wavelength selective switch wherein an input optical signal is spatially wavelength-dispersed and polarization-split in two preferably perpendicular planes. The wavelength dispersion is preferably performed by a diffraction grating, and the polarization-splitting by a polarizing beam splitter. A polarization rotation device, such as a liquid crystal polarization modulator, pixelated along the wavelength dispersive direction such that each pixel operates on a separate wavelength channel, is operative to rotate the polarization of the light signal passing through each pixel, according to the control voltage applied to the pixel. The polarization modulated signals are then wavelength-recombined and polarization-recombined by means of similar dispersion and polarization combining components as were used to respectively disperse and split the input signals. At the output polarization recombiner, the direction in which the resulting output signal is directed is determined by whether the polarization of the particular wavelength channel was rotated by the polarization modulator pixel, or not. A fast, wavelength selective, optical switch is thus provided, capable of use in WDM switching applications. Such a switch can also be provided in a 1×1 configuration, for use as a channel blocker. However, the use of two-channel input and output ports makes the switch unnecessarily complicated for such use. Furthermore, the resolution and insertion loss may be inferior to what could be achieved in a switch constructed from the outset for single pole, single channel switching.
There therefore exists a need for a fiber optical, single-pole, wavelength selective optical switch which can be manufactured inexpensively, while also being small in size for easy installation, reliable, have very low insertion loss, high wavelength resolution and stable performance over a variety of environmental conditions of the network.
The disclosures of each of the publications mentioned in this section and in other sections of the specification, are hereby incorporated by reference, each in its entirety.